1. Field of the Invention
The present invention relates to an apparatus for and a method of estimating a steam turbine output in a single shaft combined plant of a dual fuel type, an apparatus for estimating a gas turbine output, and an apparatus for controlling a single shaft combined plant of a dual fuel type.
2. Description of the Related Art
A control method for controlling a single shaft combined plant according to related art is explained with reference to FIG. 1. As shown in FIG. 1, a single shaft combined plant is a plant in which a gas turbine 201 and a steam turbine 202 are connected by a single shaft.
In the single shaft combined plant, the pilot ratio (a ratio between a main fuel flow rate and a pilot fuel flow rate) is controlled on the basis of the difference between a measured shaft output (on the MW basis) 211 of a generator G and a target generator output 211a. That is, for controlling the pilot ratio, it is enough to know the shaft output 211 of the generator G, which is the total of the output of the steam turbine 202 and the output of the gas turbine 201 (a gas turbine output 213). It is not necessary to know the output of the steam turbine 202 and the gas turbine output 213 separately.
On the contrary, an amount of air provided into a compressor C′ and an amount of air provided into a burner 314 are controlled on the basis of the gas turbine output 213 (on the MW basis). However, the gas turbine output 213 can not be directly measured. So, an operating unit 210 calculates an estimated output 212 (MW conversion) of the steam turbine, which is estimated to be outputted from the steam turbine 202. Then, a subtractor calculates the gas turbine output 213 by subtracting the estimated output 212 of the steam turbine from the measured shaft output (on the MW basis) of the generator G′.
A combustor bypass valve opening instruction 216 and an IGV opening instruction 217 are calculated so that a stable combustion situation can be obtained in a gas turbine combustor 214 on the basis of the calculated gas turbine output 213. A combustor bypass valve 220 and an IGV 221 are driven to thereby control the amounts of air introduced into the compressor C′ and the combustor 214. That is, a first function generator 204 receives a signal indicating the gas turbine output 213 and outputs a signal 216 indicative of an optimal combustor bypass valve opening. A second function generator 205 receives a signal indicating the gas turbine output 213 and outputs a signal 217 indicating an optimal IGV opening.
In a conventional single fuel type (a natural gas combustion type) single shaft combined plant using a premix burner in the gas turbine combustor 214 as shown in FIG. 2, the steam turbine output 212 is estimated on the basis of an intermediate turbine inlet steam pressure 231 by multiplying the correction values of steam temperatures 232, 233 and a steam condenser vacuum degree (steam turbine exhaust pressure) 234, in order to make efficiency high and reduce an exhaust amount of harmful substances (NOx and the like).
Hereafter, the steam turbine output 212 estimated by the method in FIG. 2 is referred to as a steam turbine output 230.
The calculating section 210 in FIG. 1 calculating the steam turbine output 212 corresponds to the part indicated by a symbol A′ in FIG. 2. That is, in the conventional art, the steam turbine output 230 shown in FIG. 2 is inputted to the subtractor 203 as the steam turbine output 212.
Here, the reason why the steam turbine output 230 can be calculated on the basis of only the intermediate pressure turbine inlet steam pressure 231 as shown in FIG. 2 is explained with reference to FIG. 3.
The flows of water and steam in the single fuel type (natural gas combustion type) combined plant is shown in FIG. 3. The flows of the water and the steam shown in FIG. 3 are basically equal to those in the single shaft combined plant and a multi-shaft combined plant.
The steam turbine output 230 is calculated by multiplying an efficiency of the steam turbine 202 by a thermal energy of the steam flowing into the steam turbine 202. The thermal energy of the steam is calculated by multiplying the steam flow rate by the steam enthalpy. Thus, the total thermal energy of the steam flowing into the steam turbine 202 is represented by the following formula:
(Flow Rate of High Pressure Steam 251)×(Enthalpy of High Pressure Steam 251)+(Flow Rate of Intermediate pressure Steam 258)×(Enthalpy of Intermediate pressure Steam 258)+(FlowRate of Low Pressure Steam 251)×(Enthalpy of Low Pressure Steam 261)
The flow rate of intermediate pressure steam 258 is represented by a function of a difference between the intermediate pressure turbine inlet steam pressure 231 and the steam condenser vacuum degree 234. Also, the enthalpy of intermediate pressure steam 258 is represented by a function of the intermediate pressure turbine inlet steam pressure 231 with correction of the intermediate pressure steam temperature 233 as a multiplier.
In the combined plant, as shown in FIG. 3, the high pressure steam 251 generated in a high pressure drum 250, after carrying out a work in a high pressure steam turbine 252, passes through a low temperature reheating steam tube 253, and joins steam 256 generated in an intermediate pressure drum 255 prior to a reheating unit 254, and then flows into an intermediate pressure steam turbine 257 as an intermediate pressure steam 258. That is, there is a relation represented by the following formula:
(Flow Rate of High Pressure Steam 251)=(Flow Rate of Intermediate pressure Steam 258)−(Amount of Steam 256 Generated in Intermediate pressure Drum 255).
Also, an amount of the steam 256 generated in the intermediate pressure drum 255 is represented by a function of a pressure of the intermediate pressure drum 255, and the pressure of the intermediate pressure drum 255 is represented by the addition of a piping pressure loss and the inlet steam pressure 231 of the intermediate pressure steam turbine 257. Thus, a flow rate of the high pressure steam 251 is represented by a function of the inlet steam pressure 231 of the intermediate pressure steam turbine 257
Also, the low pressure steam 261 is mixed with the intermediate pressure steam 258 after carrying out the work inside the steam turbine 202. Thus, the inlet steam pressure of the low pressure steam turbine 262, which serves as the function of the flow rate of the low pressure steam 261, becomes the function of the inlet steam pressure 231 of the intermediate pressure steam turbine 257.
In this way, by considering heat balance, the inlet steam pressure 231 of the intermediate pressure steam turbine 257 is related to all factors. Thus, by calculating the steam turbine output 230 as a function of the inlet steam turbine pressure 231 of the intermediate pressure steam turbine 257, the steam turbine output 230 is approximately calculated.
A combined turbine plant including a gas turbine and an exhaust gas boiler generating steam by utilizing the exhaust heat from the gas turbine and a steam turbine driven by the steam from the exhaust gas boiler and connected with the gas turbine by a single shaft is disclosed, for example, in Japanese Laid Open Patent Application (JP-A-Heisei 9-32508).